Automatic control device



Jan. 12, 1932. F. F. UEHLING AUTOMATIC CONTROL DEVICE Filed April 4, 1930 INVENTOR stares rsr oFic F 1T2 UEHLING, OF PASSAIC, EERSEY AU'LGMATIC CONTRQL I EVICE Application filed April L, 1935). Serial No. 441,702.

This invention relates to the automatic 6 being kept taut by a counter-weight 10. It control of pressure and may be applied in is thus obvious that as the motor 4 operates numerous w to automaticallymaintain the in one direction the damper 7 will slowly pressure of a fluid at some predetermined open, and as the motor operates in the oppopoint. in the particular form of the invensite direction the damper will slowly close. 55 tion herein described, I maintain a predeter- The electric circuits which operate the momined pressure in a steam boiler by autotor 3 in one direction or the other are conmatically changing the position of a damper, trolled by two relays A and B. These relays, which damper controls the heat input to the which will be presently described in detail,

In boiler. The pressure in the boiler is transare similar in construction, and consist re 60 mitted to a Bourdon spring, any change in the spectively of three tiltably mounted connecposition of which spring will open or close tors 17 19, and 20 which may be tilted by the the proper electric circuit to actuate the action of an electro-magnet 21, and three damper as required to maintain the desired tiltably mounted connectors 22, 24, and 25 pressure in the boiler. The opening and closwhich may be tilted by the action of an fia ing of these circuits is accomplished in a novel electro-magnet 26. manner by the use of a special form of relay Figures 2 and 3 illustrate connectors 17 19, in combination with a galvanometer and 20, 22, 24, and 25 in detail and in diflerent thermo-couples, all in a manner which will be POSi iODS. Each connector is of the same d ib d 1 construction and consists of mercury 27, Fig

Figure 1 illustrates the entire apparatus ure 2, hermetically sealed in a glass tube 28. diagrammatically, the relays and galvanome- 631 One end of the tube is a pocket 29. Into ter being shown in plan and the remaining the end of the tube nearest the pocket is sealed components in elevation. a wire 30 which extends into the pocket as Figures 2 and 3 illustrate two positions of illustrated and protrudes outside of the tube 7 a special form of mercury switch, three of at 31 as a means for making electrical connecwhich form part of each of the relays. The tion with the mercury inside of the tube. mercury switches will hereinafter be referred ikewise there i another Wire 32 sealed into to as connectors. l the tube at the other end, and which also ex- In Figure 1, l haveillustrated a portion of t ds i to the mercury and protrudes Outsid so a boiler 1 containing water 2. The boiler of the tube at 33 for making electrical connecnmy f any t th vygtg i hi h i tion with the mercury. It is obvious that if evapgyatgd by the heat {1 9111 a furnace 1101, the CODHGCUOI is tilted as illustrated in Figshown. The products of combustion from the 111% a e ec c Cu rent- Will he permitted to furnace leaye the boiler through a fluid 8, the flow through the mercury between 31 and 32, 55 rate of combustion in the furnac being 01 while if the connector is tilted in the opposite 3 11 b a damper 1, Th da i o 1 direction, illustrated in Figure 3, the mercated in the fine that the rate of flow of gas cury will break into two globules, some of it throughthefiuemaybeincreased or decreased re n g i the pocket 29 thus breaking respec 'ively by lowering or lifting the dampelectrical connection bet-ween 31 and 33. a0

arm 9, the damper being fully closed when The connectors 17, 19 and 20 of relay A, the arm 9 has been lifted forty-five degrees Figure 1, are fastened to a tiltable frame 3 1 from. the horizontal. The lifting and lowerwhich frame is pivoted in bearings 35 and 36. ing of the arm 9 is caused by a reversible mo- These bearings are fastened to a base plate tor 3 which communicates with a pulley 5 37. An armature 38 with which the electrothrough a properly designed reducing gear magnet 21 may react is permanently fastened in a gear case 4. To the pulley 5 is fastened to the tiltable frame 34. The tiltable frame a wire or similar flexible connection 6 which is held in its normal position by a spring 39 7 passes over guide pulleys 11 and 12, and is which pulls the armature 38 away from the fastened to the arm 9 as illustrated, the Wire magnet 21 until it touches an adjustable 1 screw 40. The tension of the spring 39 is also adjustable by means of a screw ll. Both screws 40 and 451 are supported by a bracket 52 which bracket is fastened to the base plate 37. The magnet 21 is also fastened to the base plate 37 by means of a bracket l2. It thus followsthat when themagnet l. is energized, the tiltable frame: 3%, including the connectors 17, 19, and will be tilted in one direction by reaction with the armature 38, and when the magnet 21 is deenergized, the frame 34 and its connectors will be tilted back to normal position by the spring 39', in which position as previously stated, the armature o8 rests against the adjusting screw all).

In like mannerthe connectors 22,,2 l, and-- of relay B ,are fasteued to a til-table frame 43 which frameisipivotcd in bearings M and 5. Thesebeari'ngs are fastened to a base plate l6. An armature 4L7. with; which the electro-magnet 26; may react is, permanently fastened to the tictable frame 13. The tiltable frame 43 is heldjin its normal position by spring :8

which pulls the armature 47 away from the magnet 26 until ittouches an adjustable screw 51. The tension of the spring 48 isalso adjustable. by wmeans of a -screw 50. Both screws 50 and 51 are supported-by a bracket 134- which bracket is. fastened to. the base plate 46.: The magnet 26 is also fastened to the base plate 46 by meansofabracket 53. It thus followsthatwhen themagnet 26 is energized, the til'table frame 4-3,, including. its

connectors 22, 2 land. 25 willbe tilted-in one direction by-reactionwiththe armature 4:7, and when themagnet 26 is:deenergized,:the frame 43 and-its connectors will be tilted back to normalposition by the spring 48, in .which position,- as preuiously stated, the armature 4:7 rests against the adjustable screw 51.

Connectors '17, 19 and-2O of relay A are fastened to the tiltable frame 34 by means of a clamp 5% :The connectors: 19 and 20 are fastened insuch apositio-n thatelectrical connection is made'through the mercury, as illustrated Figure 2, when they are tilted by the magnet 21, and that electrical connection isbroken through the mercury, as illustrated in Figure 3', when they. are tilted back to normal positioniby the spring 39. On the other hand, connector 17 is fastened: to the tiltable frameiso that when tilted by thevmagnet 21, electrical connection through the mercury will bebroken as illustrated in Figure: 3,, and when tilted back to normal position, by the spring 39:, electrical connection. ismade through the mercury as illustrated in Figure 2. 1 f

Similarly connectors 22, 2:4: and-2570f relay B are fastened to the tiltable. frame 4L3 by means of a-clamp-55]; The connectors 24 and 25 are fastenedinsuch a position that electrical "connection is made through the mercury, as; illustrated in Figure 2, when they are tilted by themagnet 26, and that electrical connection is broken through the mercury, as illustrated in Figure 3, when they are tilted back to normal position by the spring 48. On the other hand, connector 22 is fastened to the tiltable frame 43 so that when tilted by the magnet 26, electrical connection. through the mercury will be broken as illustrated in. Figure. 3, and \VllGILtlltQd back to normal position by the spring 4E8, electrical connection is made through the mercury as illustrated in Figure 2. In order to facilitate the tracing of the different circuits which include the connectors I have labeled each. connector with an arrow. Those connectors whose arrows point in the direction. of tilting as caused by the magnet, close a circuit When-tilted by the magnet, andopen the circuit when. tilted bythe spring, while those; connectors Whose arrows point in the dircctionof tiltingascausedby the spring, open circuit when tilted bythe magnet and close the circuit when, tilted by the spring.

, It thus follows, that whenmagnet21 is energized, the circuit, through cannectorgs 19 and 20:will' be. closed, and that when magnet 2 6. is energized, the circuit through connectors 2 L andi25' will becl os e d. These connectors 19 and 20, and 24 and 2-5 constitute a revcrsingswitch. for the motor 3., This motor is series wound. and is operated from any source of current as from abattery 1 13.: The wiresllet andllb are connected. with the brushes-ofthe motor while the wires116. and

117' are connected with the field. The wires which connect the motor with connectors 19 and 2.0 of rela5 A, andlconnectors 24 and 25 of relay B, are shown heavy lines to con trast them from the rest of'thecircuits. They are connected in the-well known manner so that when; the circuit isiclosed through the connectors 19 and 20by theaction of magnet 21, the motor will -un inone direction, and when the circuitisvclosed through the connectors 24 and 25 by the actionofmagnet 26, the motor will, runinthe opposite direction.

. Ellh,8150f the electric circuits which actuatesthe magnet-21 or magnet 26 may be closed by theindicatingneedle 5.6 ofa galvanometer 57. The'galvanometer 57 is of the well 1 vKnown.v formwvhich consists of a permanent magnet. 'Tlbetween the poles of which is pivoted a 0011,75. The indicating needle 56 is attached to-the' pivoted coil in the usual manner while the turning moment of the coil as causedby the current passing through it, is;counteri-balanced by. a hair spring 76. The circuit. which includes the magnet 21 of relay A is closed. by electrical contactbetween the needle-5.6 and a contact disc 61. The con tact disc :61 is carkied by an adjustable rod 58 which is mounted'on an insulated support 59. Thetcircuit hichincludes the magnet 26 of relay B is closed-byelectrical contact between theneedle 56 anda contactdisc 64, the contact disc 64 being carried by an ad- Y 7 discs 61 and64 is assured,

justable rod 62 which is mounted on an insulated support 63. The circuit which energizes the magnet 21 of relay A starts at battery 65, thence through wire 79 to a limiting switch which will be reii'erred to later and which consists of a blade spring 64: to which is fastened a contact piece 129, and a second contact piece 130 fastened to a stationary arm From the limiting switch the circuit continues through wires 23 and 18 to a binding post 71, rom the binding post 71 through an electrical resistance 72 (to be referred to later) to a binding post '23, from binding post 7'3 through the hair s1 ring 76 of the galvanometer to the needle VJ hen the needle 56 touches the contact disc 61, the circuit-con- .tinues through the rod 58, and wire66 to a binding post 67, from the binding post- 67 through a flexible connection 68, the connector 17 and a flexible connection 69 to the magnet 21, and from magnet 21 through wire 70 baclr to the. battery 65. Similarly the circuit which energizes the magnet 26 of relay B starts at battery 60, thence through wire 88 to a limiting switch which ill he referred to later and which consists of a blade sprin 85 to which is fastened a contact piece 128, and asecond contact piece 127 1" oned to a stationary arm From the limiting switch the circuit continues through wire 18 to the binding post 71, from the binding post 71 through the electrical resistance 72 to the binding post 7'3,

from binding post 73 through the hair spring it of the galvanometer to the needle 56.

When the needle touches'the contact disc 64; the circuit continues through rod 62 and wire 77 to a binding post 78, from the binding post 7 8 through a flexible connection 19, the

' connector 2; and a flexible connection 80 to i the magnet 26, and from magnet 26 through wire 81 back to the battery 60. The manner in which the relays A and B function depending upon whether the needle 56 of the galyanometer touches the disc 61 or 6 1, and the manner in which electrical contact between the needle 56 and one or the other of the will be presently described in complete detail.

The current which deflects the needle 56 ot the galranometer is created in two thermocouples 90 and 91 which are connected in op- )osition as illustrated. includes the ire mice 91, througn wire 9. to the binding post 71, from binding post 71 through the resistance 72 to binding post 73, from the binding post ('3 to the hair spring '56 from the hair sp 3 6 through the pivoted coil 75 to'hinding pos 89, from binding post 89 through wire 9. to the lead 92 and thence bacl; to he couples. The thernio-couples 90 one 1 are lzept at constant temperature, or nearly so, by an -couplcs and the galva- 3 electric heating coil which receives its The circuit -which ti om the lead 95 of couple power from any source as from a battery 13 through wires 1 and 16. The-couples are electrically opposed to each other as will be noted from the plus symbol on each of the leads 92 and 95, and the minus symbol on each of the loads 93 and 94:. In other words the couples 90 and 91 are so included in the circuit with the galvanonieter that the electro-motive force of one of the couples neutralizes the electro-motivc force of the other. The deflection of the galvanometer inone direction or the other as caused by the thermo-couple, depends upon the shortcircuiting of one or the other of the couples, all in a manner to be presently described.

The difiiculty of making electrical contact between two contact surfaces by means of a delicate pressure such as exerted by the delicate needle 56 of the galvanometer against one or the other of the discs 61 and 6 1 has long been rea ized. It is to eliminate this dii'iiculty that I have provided the electrical resistance already referred to. The trouble that is experienced when a delicate needle is used to close an el ctric circuit, as for example when the needle 56 is deflected against the disc 61, is that the delicate pressure cX erted by the needle against the disc is not sufficient to permit the required amount of current to flow. The circuit which is closed contact between the needle 56' and the disc 61 includes the connector 17 and magnet 21 of relay A, also battery and the resistance 72. This circuit has already been traced. Although the delicate pressure between the needle 56 and the disc 61 may not cause sufiicient current to flow to actuate the magnet 21, it will net-'ertheless cause some current to flow through. the circuit which includes the connector 17', magnet 21, batter '65, resistance 72, hair spring 76, needle 56, and disc 61. Regardless of how small this flow may be, it will obviously cause a drop or difference in potential across the resistance 72. This drop or difference in potential will cause a slight flow of current from the resistance through binding post 73, the hair spring 76 and the pivoted coil 7 5 to binding post 89, from binding post 89 through wire 97 and lead 92 to couple 90, from couple 90 through the leads 93 and 9a to couple 91, and from couple 91. through the lead 95, wire 96 and binding post 71 back to the resistance. The polarity of battery 65 is such that the flow of current just described is in the proper direction through the galvanometer to to co the needle 56 tighter against the disc 61. The increased pressure between the needle 56 and the disc 61 will increase the flow through the magnet 21 and through the resistance 7 2. The increased flow through the resistance 72 will again increase the drop across the resistance which, in the manner just described, will gain increase the pressure between the needle 56 and the disc 61, and this increased pres- Lil ' the sprin in potential across the sure will obviously still further increase the flow of current through toe circuit which inl i I n .lm'sicludcs tile magnet 21 and M13 lcolb'ollnse (2.

In other words as soon as there is the slightest contact between the needle 56 and the disc 61, the pressure bet ween the needle and the disc will instantly build up, in the manner just described, suflicient curren -flows Ulitil E L1 1 V through the nia 'net .cl to tilt inc conne-ctois and permitting nectors back to lposition. 36 still touches i the same action will repeat itself. ores so long as the needle 56 touches 61, so long will the r J A continue deenerg to osci 7 l l- L 1 oscillation or tne relay ii lil. alternately close and open the circuit through the con- 1 l which cir Y i to close the manner, the circuit which is closed 1 between the nee lle and the disc .s the connector 22 and magnet 26 v also battery 6i and resistance 72. This circuit has already been traced. Although is delicate pressure between the needle 58 and the disc o may not cause sufficient cu ent to flow to actuate the magnet 26, it Will neve eless cause some current to "hrougli t it which includes the i: O a, batery 69, resistance 72, hair spr j 76, needle 56 and disc 6 1. Regardless of 4 small this flow may be, it will obviously cause a dr p or dilierence resistance 72. This drop or diilerence in potential will cause a slight flow of current from the resistance through bindi post '71, wire 96 and lead 95 to couple 91, from couple 91 through leads 9%- aju to couple 99, "from. couple 90 through lead 92and 9? to binding post 89, and i n "inding post 89 througu the pivoted coil 75, hair spri 7G and binding i c i ceased pressure we. obviously sill ier increase the flow of current through the circuit which includes the magnet 26 the resistance 72. In other words as soon as there is the slightest v 1 7'1. in the manner 111st described. inc 7 contact between the needle 56 and the disc 64, the pressure between the needle and the disc will instantly build up, in the manner just described, until sufficient current flows through the magnet 26 to tilt the connectors 22, 24c and 25 of relay B. As soon as connector 22 has been tilted, the circuit through it and the magnet 26 will be broken, thereby deenergizing the magnet26 and permitting the spring 48 to tilt the connectors back to normal position. If the needle 56 still touches the disc 64-, the same action will repeat itself. In other words so long as the needle 56 touches the disc 64, so long will the relay continue to oscillate in the manner just described. The oscillation of relay B will alternately close and open the circuit through the connectors 24 and which ci" cuit as previously described operates the mo tor 3 in the proper direction to open the damper 7.

The needle 56 of the galvonomete'r is so adjusted that its Zero position is midway between the dis-cs 61 and 641. In other words when there is no current flowing through the galvanometer, the position of the needle with respect to the contact discs will be as illustrated. It is obvious that if the couples 90 and 91 have the same characteristics, and if, as previously stated, they are electrically opposed as illustrated, then the electro-motive force 01"" one neutralizes the e1ectro-1notive force of the other, irrespective of the temperature to which the couples may be heated by the heating coil 15 already referred to. On the other hand if the couple 91 is short-circuited as for example through wires 98 and 190, then the neutralizing effect of couple 91 will be eliminated and the electroqnotive force of the couple 90 will be permitted to send a current to the galvanometer through the circuit already described. Likewise if the couple 90 is shortcircuited as for example throu h wires 99 and 100, then the neutralizii'ig e root of the couple 90 will be eliminated and the electro-niotive for'ceof the couple 91 will be permitted to send a current through the galvanometer. The polarity of the couple 90 is such that when the couple 91 is short-'circuited, the current from couple 90 will deflect the needle 56 of the galvanometer against the disc 61 thereby when the couple 90 is shortcircuited, the

current from the couple 91 will deflect the needle 56' of the galva-nometer against the disc 64, thereby closing the circuit which includes the connector 22 and magnet 26, which circuit, in a manner already described, 210- tuates the relay B to operate the motor 3 in the proper direction to open the damper 7 lVhethcr the couple 90, or the couple 91 is short-circuited depends upon whether the pressure in the boiler is below or above the predetermined pressure at which the steam in the boher is to be maintained. This is accomplished by means of a Bourdon spring 10. which is connected with the pressure in the boi'er through the tube 101. The tube 101 communicates with the Bourdon spring 107 through a hollow casting; 108 which is held rigidly in place against the gear case 41 by means of a bracket 109. To the movable end of the Bourdon spring is fastened an extension arm 10% which extends to a point between two electrical contact screws 121 and 122 as illustrated. These screws are respectively carri d bytwo extension arms 106 and 105. These arms are electrically insulated from each otheran d are supported in a manner which will be presently described. The arm 106 is electrically connected with the positive lead of the couple 91 through a flexible connec ion 98, while the arm 105 is electrically connected with the positive lead of the couple 90 through a flexible connection 99. The extension arm 10% which extends from the Bourdon spring 107 to a point between the two contact screws 121 and 122 is on the other hand electrically connected with the negative lead of each couple through the ground wire 100. The contact screws 121 and 122 are so adjusted that when the steam in the boiler is at the desired or predetermined pressure, the arm 104 will be very close to the extremity of each of the screws but touching neither of them. It thus follo that when the steam is at the pre' determined pressure, neither of the couples will be short-circuited, there will be no flow through the galvanometer, and the needle 56 will. be at Zero or midway between the two contact discs 61 and 61. In this position of the needle 56, neither of the relays A and B will be actuated and the motor 3 will consequently be dead. On the other hand if the pressure in the boiler rises slightly above the u-edetcrmined pressure, the Bourdon spring will obviously lift the arm 104C thereby establishing electrical contact between said arm and the screw 121. This contact short-circuits the couple 91 thus permitting the couple 90 to deflect the needle 56 against the disc 61. Contact between the needle 56 and the disc 61 actuates the relay A which operates the rotor 8 in the proper direction to close the damper thereby decreasing the pressure in the boiler. Liluwise if the pressure in the boiler drops slightly below the predetermined pressure, the Bourdon spring will obviously lower the arm 104, thereby establishcontact between said arm and the screw 122. This contact short-circuits the couple the needle 56 against the disc 64. Contact between the needle 56 and the disc 6a actuates the relay B which operates the motor 3 in the proper direction to open the damper thereby increasing the pressure.

It is obvious from the above that when the pressure in the boiler is at a predetermined point the motor 3 which operates the damper will be dead but when the pressure in the boiler is below the predetermined point, the motor will operate to open the damper, and when the pressure in the boiler is above the predetermined point, the motor will operate to clo e the damper, all in the manner above described. It is however further obvious, that it takes some time for any boiler to re spond to a definite change in damper adjustment. In other words a slight drop in the boiler pressure below normal might cause the damper to open full before the pressure responds to the increased heat input as caused by the wider damper opening. Likewise an increase in the pressure might cause the damper to close full or nearly so before the pressure responds to the decreased heat input as caused by the closing of the damper. Such action of the damper beyond the necessary point to produce the required result is what is known in practice as hunting action which is decidedly objectionable and detrimental to good control. To prevent such hunting, and to make it possible for the damper to open or close to the exact position required to maintain the pressure constant within very narrow limits under varying load conditions, I provide a wheel 118 which supports the insulated arms 105 and 106 already referred to. The wheel 118 is on the same shaft with a worm wheel 119. said shaft being carried in a bearing supported by a bracket 111, which bracket is fastened to the base 126 as illustrated. The worm wheel 119 meshes with a worm 1.20 which worm is fastened to the same shaft with the pulley 5. The wheel 118 will therefore turn in proportion to the motion of pulley 5, thereby lifting or lowering the contact screws 121' and 122 through an arc with the worm wheel 119 as a center. The wire 6 which connects the pulley 5 with the damper is so fastened to the pulley that as the motor 3'operates to open the damper, the contact screws 121 and 122 will be lowered, and when the motor operates to close damper, the whe'el 1 18 turns in a clockwise direction, thereby lifting the arms 106 and 165 with tl'ieir respective contact screws 121' and 122. The closing action of the damper will continue only untihcon-tact between the arm 10-1 "and the screw 121 is again broken at which time the galva-nometer needle will againassume its normal position, as illustrated, thus causing the motor to stop. If theclosin' of the damperby theaction oft-he motor to this point is not suiiicient to prevent'awfurther increase in boiler pressure, thenthe increasing boiler pressure will again. cause contact between the arm 10% and the contact screw l21,-and the 'motor will continue-tooperateto close the damper, at' the same time still further lifting the screws 121 and 122 until contact-between the arm 104s and the screw 121 is again broken, at which time the motor will stop. If thenew' position of the damper now z revents a furtherfin- Grease-in the boiler pressure, itis'obi ious that the i position of the damper will remain un changed. Likewise if the pressure in the boiler'decreases,tlie Bourdonespring will con-- tract thereby lowering the arm" 10 lwhich consequently makes contact with the screw 1:22; l he electrical contact thus established short 'circuits "the coupleQO which'in the man ner' a lready stated '=per-Inits the couple 91 to deflect thegalranometer needle, 56: against the disc 65 which oloses the circuit to operate the motorin the proper direction to open the'dampcr. 'As-thepulleyb"tulms to open. the da mpergthe wheel M8 turns in. amount/er.- clookwise di rect-ion,- thereby :loweri arms-106' and 105 with their respec Wenontact screws 121 and 12;. "The opening action o'f the damper will continue only until contact between the arm 10d and the screw 122 isagain broken at which time the :g'a'lvanometerneedle' will again'assume-its normal positiongas illustrated, thus causing; the motor'to stop. 1 H the ope'ning of thewlamperby the action of the motortothis point is not sufficient to prevent a further decrease in the boiler pressure, then thedecreasing boiler pressure will again oause'contact between the arm 1 10a and itherontact screw 122, :and the motor will: continue to operatcto open the damper, at the same timestill further lowering the screws 1L1 and 122 until' contact between the arm '104:=ancl'-the screw'122 is again =brohen -at which the motor will stop. If the new positioned. the damper now prevents a further decrease in the boiler pressure, it is obvious that-the position *otthe:

damper will remain unchanged. *Itisevident from'the' "above that by changing the positi'on' of the contact screws 'l-21 an'd 12 in the:

manner described; damper will open or close only to a point where the heat input as controlled by the d amper is 'balancedibythe actual load on the boilerythus eliminating excessive damper motion as would otherwise be caused by the lag in the rboilerto respond to changesin the damper position.

:In order to prevent the operation of the damper beyondthe position in which it is fully closed, or beyond the position in which it is fully open, I provide two limiting switches which have already been referred to, oneot whiclnis included in 'thecircu'it with relay Arand theother of which is included in the circuit with relay B. These switches are operated by a ball 86 fastened to the flexible wire 6. The Wire-6 passes through a hole or slot in. the blade spring 8d of the switch which limits the opening motion of the damper.- Thiscswitchais fastened to a stationary rod-87 andis adjusted to the proper position with respectto the ball 86 so that as'the ball rises due 'to the damper opening actionof the-imotor, it will lift the blade spring '84 immediately after the damper is fully open. The lifting of 'the blade spring 84 breaks contaot between the two contact pieces 129xand 130 thus opening the circuit which includes the relay A. The Opening of this circuit will obviously stop the .damper opening action ofthe motor even though the needle 56 of'thegalvanometer may still be touching the "contact disc 61 Likewise the wire 6 passes throng-ha hole or slot of the blade 85 of t-heswitch which limits the closing m'otionofthe damper. This switch is also fastened to therod:87 and is adjusted to the proper position with respect to the ball 86 s0 that as the ball is lowered due to the damper closing action'ofthe motor,'it will push down the blade spring 85 immediately after-thedamper is fu'llyclose'd. The pushing down of the blade spring 85 breaks'contaotbetween th'e contact pieces 127 and 128 thus openi -ng the circuit which includes the relay B. Theopen-ing of this circuit will obviously stop the damper closing action of the motor eventhough the needle 56 of the galvanometer may still be touching the contact disc 64:.

Although "I have utilized a 'Bourdon spring as a matter of convenience in illustrating this invention, it is obvious thatany movable element which is affected by changes in pressure may be used in place thereof for moving "the arm 104 with respect to the contact screws. As-substitutes for the Bourdon spring I might mention as examples, a piston, 21 diaphragmya bel-lo-w,-0ra mercury column, any of which might be used instead of the Bourdon spring without in any way departing from the novelty-of this invention. Furthermore although I have described-only one application of this inventiom there are obviously many others as for example, the automatic throttling of an inlet -'or outlet valve of a pressure chamber for the purpose of keeping a constant pressure within saidchamber.

Whatl claim-as new and desire to cover by rLttcr-s Patent is: l

(ill

1. In a device of the class described, the combination with a chamber, of a movable element connected with the chamber and actuated by the pressure in the chamber, a con tact piece with which the movable element makes electrical contact, two electrically opposed thermo-couples, a circuit which includes said couples, and a circuit which in cludes the movable element, the contact piece, and one or" the thermo-couples.

2. In a device of the class described, the combination with a chamber, of a movable element which communicates with the chamher and is actuated by changes of pressure in the chamber, a contact piece with which the movable element makes electrical contact when reaches a predetermined position,

two electrically opposed thermo-couples, a circuit which includes said couples, a circuit which includes the movable element, the con tact piece and one of the thermo-couples, a second contact piece with which the movable elementmakes electrical contact when it reaches a second predetermined position, and a circuit which includes the movable element, the second contact piece and the other thermo-couple.

3. In a device of the class described, the combinattion with a chamber, of a movable elem nt actuated by changes of pressure in the chamber, a contact'piece with which the movable element makes electrical contact when it reach s a predetermined position,

two electrically opposed thermo-couples, a

circuit which includes the movable element, the contact piece and one of the thermocouples, a galvanometer, and a second circuit which includes both thermo-couples and the u'alvanometer.

7 4 In a device of the class described, the con ation with a chamber, of a movable eletuated by changes of pressure in the chamber. a contact piece with which the movable element makes electrical contact when said element reaches a. predetermined position, two electrically opposed thermo-couples, a circuit which includes the movable element, the contact piece, and one of the thermo-couplcs, second contact piece tor making elecll al contact with the movable element when said clementreaches a second predetermined position, a second circuit which includes the movable element, the second contact piece, and the other t-hermo-couple, a galvanometer, and third circuit which includes both therinc-couples and the ,Q alvanometer.

in a device the class described, the combination with a chamber, of a movable element actuated by changes oi pressure in the chamber, a contact piece with which the movable clement makes electrical contact when sai d element reaches a predetermined position, two electrically opposed thermocouples, a circuit wlnch includes the movable element, the contact piece, and one of the thermo-couples, a second contact piece for making electrical contact with the movable element when said element reaches a second predetermined position, a second circuit which includes the movable element, the second contact piece, and the other thermo-couple, a galvanometer, a third circuit which includes both thermo-couples, and the galvanometer, and means for heating the thermo-couples.

G, In a. device of the class described, the combination with a chamber, of a movable element actuated by changes of pressure in the chamber, a contact piece with which the r ovable element makes electrical contact said element reaches a predetermined poi; ion, two electrically opposed thermocouples, a circuit which includes the movable element, a contact piece, and one of the thermo-couples, a second contact piece for making elect *ical contact with the movable element when said element reaches a second predetermined position, a. second circuit which includes the movable element, the second conta piece, and the other thermo-couple, a galvanometer, a tliird circuit which includes both thermocouples and the galvanometer, means for heating the thermocouples, and a motor the operation of which is controlled by the third circuit.

7. In aoevice ot the class described, the combination with a chamber, of a Bourdon spring; connected with the chamber, a contact piece with which the Bourdon spring makes electric contact when the pressure in the chamber reaches a predetermined point, two electrically opposed thermocouples, a circuit which includes one oi the thermo-couples, the contact piece and tne Bourdon spring, a galvanometer, and a second circuit which includes the galvanometer and the thermo-coupics.

8. In a device of the class described, the combination with a chamber, of a Bourdon spring connected with the chamber, a contact piece with which tl e Bourdon spring makes electrical contact when the pressure in the chamber reaches a predetermined point, two electr'cally opposed thermo-couples, a circuit which includes one of the thermo-couples, the Bourdon sp ing, and the contact piece, a second contact piece with which the Bourdon spring makes electrical contact when the pressure in. the chamber reaches a second predetermined point, a second. circuit which includes the other thermo-couple, the second contact piece and the Bourdon spring, a galvanometer, and a third circuit which includes the galvanometer and both thermocouples.

9. In a device of the class described, the combination with a thermocouple, of a second thermo-couple in series with, but electrically o1 posed to the first thermo-couple, a galvanometer, a circuit which includes the galvanometer and the two thermocouples, a chamber, a movable element actuated by the ond thermo-co: changing the re l contact pieces with movable element, independently of l c i in the chamber.

10. o a device the Claws described, the ,ation with a steam boiler, of a damper lling the heat input to the boiler, a c. ement connected with and actuate the p e ure within the boiler, a contact piece with which the movable element ma res contact when id element reaches a predetermined 1011, two electrically opposed thermocou les, an electric circuit which ineludes one of th thermocouples, the contact piece, and the movable element, a second contact piece w which the movable element makes electrical contact when said element reaches a second predetermined position, a second circuit which includes the other thermocouple, the second contact piece and the movable element, a galvanometer having an indicating needle, :1 third electric circuit which includes the galvanoineter and the two thermo-couples, a motor onnected with the damper for operating same, contact disc with which the needle of the galvanometer collides when deflected in one direction, a fourth circuit which includes the needle and the contact (11.3: and which circuit controls the operation of the motor to close the damper, a second contact disc with which the needle of the galvanometer collides wh n deflected in the opposite 'cction, and a fifth circuit which includes the needle and tie second con tact disc and which circuit controls the operation of the motor to open the damper.

11. In a device of the class described, the combination with a steam boiler, of a damper for controlling the heat input to the boiler, a movable element connected with and actuated by the pres e within the boiler, a contact piece with i iich the movable element makes contact w a said elunent reaches a predetermin d position, two electrically opposed theru'io-cou" les, an electric circuit which includes one of the thermo-couples, the contact piece, and the movable element, a second contact piece with which the novabl element n'ialres electrical contact when element 1. hes a second predetermined position, a

second circuit which include the other thermo-couple, the second contact piece and the movable elemen t, a galvanometer having an indicating needle, a third electric circuit 1 which includes the galvanometer and the two thermo-couples, a motor connected with the damper for operating same, a contact disc with which the needle of the galvanometer collides when deflected in one direction, a fourth circuit which includes the needle and the contact disc and which circuit controls the operation of the motor to close the damper, a second contact disc with which the needle of the galvanometer collides when deflected in the opposite direction, a fifth circuit which includes the needle and the second contact disc and which controls the operation of the motor to open the damper, and a connection between the motor and the contact pieces for changing the position of said pieces in proportion to the number of revolutions of the motor and independently of the pressure in the boiler.

12. In a device of the class described, the combination with a steam boiler, of a damper for controlling the heat input to the boiler, a movable element connected with and actuated b the press within the boiler, a contact piece with which the movable element makes contact when said element reaches a predetermined position, two electrically opposed thermocouples, an electric circuit which includes one or" the thermo-couples, the contact piece, and the movable element, a second contact piece with which the movable element makes electrical contact when said element reaches a second predetermined position, a second circuit which includes the other th rmocouple, th I second contact piece and the movable element, a galvanometer having an indicating needle, a third electric circuit which lClLlQlQS the galvanomcter and the two thcrmo-couples, a. motor connected with the damper for operating same, a contact disc with which the needle of the galvanometer collides when deflected in one direction, afourth circuit which includes the needle and the contact disc and which circuit controls the operation of the motor, to close the damper, a second contact disc with which the needle of the galvanometer collides when deflected in the opposite direction, a fifth circuit which includes the needle and the second contact disc and which controls the operation of the motor to open the damper, a connectionbetween the motor and the contact pieces for changing the position of said contact pieces in proportion to the number of revolutions of the motor and independently of the pressure the chamber, a switch in the fourth circuit for opening and closing said circuit, an element for actuating said switch, operated by the motor, a second switch included in the fitth circuit, and an element for actuating the second switch, operated by th e motor.

18. In a device of the class described, the combination with a chamber, of a movable element connected with the chamber and actuated by the pressure in the chamber, an electrical contact piece with which the movable element makes electrical contact when it reaches a predetermined position, two electrically opposed thermo-couples, a circuit which includes one of the thermo-couples, the contact, and the movable element, a second electrical contact with which the movable element makes electrical contact when it reaches a second predetermined position, a second circuit which includes the other thermo-couple, the second contact and the movable element, a galvanometer having an indicating needle, an electrical resistance, a third circuit which includes the galvanom'eter, the resistance, and the two thermo-couples, a contact piece with which the galvanometer needle makes el ctrical contact when deflected in one direction, a fourth circuit which includes the galvanometer needle, the contact piece and the resistance, a second contact piece with which the galvanometer needle makes electrical contact when deflected in the opposite direction, and a fifth circuit which includes the galvanometer needle, the second contact piece, and the resistance.

14. In a device of the class described, the combination with a chamber, of a movable element connected with the chamber and actuated by the pressure in the chamber, an electrical contact with which the movable element makes electrical contact when it reaches a predetermined position, two electrically opposed thermo-couples, a circuit which, includes one of the thermo-couples, the contact, and the movable element, a second electrical contact with which the movable element makes electricalcontact when it reaches a second predetermined position, a second circuit which includes the other thermo-couple, the second contact and the movable element, a galvanometer having an indicating needle, an electrical resistance, a third circuit which includes the galvanometer, the resist ance, and the two thermo-couples, a contact piece with which the galvanom'eter needle makes electrical contact when deflected in one direction, a fourth circuit which includes the galvanometer needle, the contact piece and the resistance, a second contact piece with which the galvanometer needle makes electrical contact when deflected in the opposite direction, afifth circuit which includes the galvanometer needle, the second contact piece, and the resistance, a damper for throttling the flow of gas through a flue, a motor connected with the damper for actuating same, the operation of said motor in one direction being controlled by the fourth circuit, and in the opposite direction by the fifth circuit.

15. In a device of the class described, the combination with a tiltable member, of an electro-magnet for tilting the member in one direction, a spring for tilting the member 1n the opposite direction, a switch actuated by the tiltable member and which is opened by the tiltable member when said member is tilted by the magnet, and closed by the tiltable member when said member is tilted by the spring, a galvanometer having an indicating needle, a contact piece wi h which't-he needle makes electrical contact when deflected in one direction, an electrical resistance, 'a circuit which includes the needle, the contact piece, the resistance, the magnet and the switch, a second tiltable member, second electro-magnet for tilting the second tiltable member in one direction, a second spring for tilting the second tiltable member in the opposite direction, a second switch actuated by the second tiltable member and which switch is opened by the member when said member is tilted by the second magnet, and closed by the member when said member is tilted by the spring, a second contact piece with which the needle of the galvanometer makes electrical contact when deflected in the opposite direction, a second circuit which includes the needle, the second contact piece, the resistance, the second magnet and the second switch, two electrically opposed thermo-couples in series, a third circuit which includes the thermocouples, the resistance and-the galvanometer, a chamber, a movable element connected with the chamber and actuated by the pressure therein, an electrical contact with which the movable element communicates when said element reaches a predetermined position, a fourth circuit which includes one of the ther- BIO-(301113168, the contact and the movable element, a second electrical contact with which the movable element communicates when said element reaches a second predetermined position, and a fifth circuit which includes the other thermo-couple, the second contact and the movable element.

16. In a device of the class described, the combination with a pressure chamber, of a Bourdon spring connected with and actuated by the pressure in the chamber, two electrical 1 contact screws, an arm fastened to the Bourdon spring and extending between the two screws, a motor, a connectionbetween the motor and the screws for changing the position or" the screws with respect to the arm, two electrically opposed thermo-couples, an electric circuit which includes one of the couples, one of the screws, and the arm, a second electric circuit which includes the other couple, the other screw andthe arm, a galvanometer, and a third circuit which includes both couples and the galvanometer, said third circuit controlling the operation of the motor.- V

717. In a device of the class described, the combination with a galvanometer having an indicating needle, of a contact piece with which the .needlemalies electrical contact when deflected in one direction, a second contact piece with which the needle makes electrical contact when deflected in the opposite direction, an electrical resistance, a motor, a relay with a primary and a secondary circuit, the primary circuit of which relay includes the needle, the first contact piece and the resistance, and the secondary circuit of which relay includes the motor to operate it in a given direction, a second relay having a primary and secondary circuit, the primary circuit of which relay includes the needle, the second contact piece and the resistance, and the secondary circuit of which relay includes the motor to operate it in the opposite direction, two electrically opposed thermocouples, a circuit which includes the thermocouples, the resistance and the galvanometer, a chamber, and means for short-circuiting one or the other of the thermocouples, said means being actuated by the pressure in the chamber.

18. In a device of the class described, the combination with a galvanometer having an indicating needle, of a contact piece with 'which the needle makes electrical contact when deflected in one direction, a second contact piece with which the needle makes electrical contact when deflected in the opposite direction, an electrical resistance, a motor, a relay with a primary and a secondary circuit, the primary circuit of which relay includes the needle, the first contact piece and the resistance, and the secondary circuit of which relay includes the motor to operate it in a given direction, a second relay having a primary and secondary circuit, the primary circuit of which relay includes the needle, the second contact piece and the resistance, and the secondary circuit of which relay includes the motor to operate it-in the opposite direction, two electrically opposed thermocouples, a circuit which includes the thermocouples, the resistance and the galvanometer, a chamber, means for short-circuiting one or the other of the thermo-couples, said means being actuated by the pressure in the chamber, a flue, a damper for throttling the flow of gas through the flue, and a connection between the motor and the damper for operating the latter.

19. In a device of the class described, the combination with a galvanometer, having two connecting terminals, of two thermocouples, the negative leads of which are electrically connected, the positive lead of one of which is connected with one of the terminals of the galvanometer, the positive lead of the other of which is connected with the other a terminal of the galvanometer, a chamber, a

Bourdon spring connected with the chamber and actuated by the pressure therein, a contact piece with which the Bourdon spring makes electricalconnection when it reaches a given position, a circuit which includes the Bourdon spring, the contact piece, and one of the couples, a second contact piece with which the Bourdon spring makes electrical connection when it reaches a second given position, a circuit which includes the Bourdon spring, the second contact piece and the other couple, a throttling means for changins 

